Coated belt and method of making same for continuous metal casting process



' Jan. 5, 1965 s. H. ROCHESTER ETAL 3,163,395

COATED BELT AND METHOD OF MAKING SAME FOR CONTINUOUS METAL CASTING PROCESS Filed June 23, 1961 Fit. 1.

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ATTORNEY United States Patent 3,163,396 CDATED BELT AND METHDD 0F MAKFNG SAME FOR CGNTINUGUS METAL CAST KG PRGCESS Stanley Herbert Rochester and Stanton Evan .i'aeir, Kinmton, (intario, Canada, assignors to Aluminium Laboratories Limited, Montreal, Quebec, Canada, a corporation of Canada Filed June 23, 1961, Ser. No. 119,131 7 Claims. (Ci. 22-5724) This invention relates to the casting of metals. More particularly, this invention relates to compositions, such as belt dressing compositions, useful in a continuous metal casting operation, such as in a metal casting process wherein molten metal is poured or continuously introduced be tween two synchronously moving endless metal belts, the opposed surfaces of the metal belts between which the molten metal is introduced serving as a mold for the solidification of the molten metal.

Still more particularly, this invention relates to a belt dressing composition suitable for use in the so-cailed Hazelett continuous metal strip casting process and apparatus for the casting of aluminum, aluminum alloys and the like. In the Hazelett process, as it has become known and used, molten metal, such as aluminum, is introduced at one end of the casting machine between two continuous ly and synchronously moving fiat metal, usually mild steel, strips or belts. The belts, generally horizontal, but traveling downward together at a small angle, are vertically spaced to define the desired thickness of the strip or slab to be produced, and are cooled on their outer surfaces, through the casting region, by large flows of water. As the molten metal is introduced between the belts and held by moving dams at the sides, it is cooled and at least partially solidified by contact with the belts while being carried forward on the moving belt upon which the metal is deposited, so that with suitable control or setting of the distance between the opposed surfaces of the moving belts a solid, cast metal strip of substantially uniform dimensions and substantially free of any surface defects is produced and removed from the other end of the casting machine. Certain forms of belt casting apparatus are shown in US. Patents Nos. 2,640,235 and 2,904,860, issued to C. W. Hazelett on June 2, 1953, and September 22, 1959, respectively, but Hazelett machines now in use embody further improvements, in cooling and otherwise, and are arranged, as in the second cited patent, to keep the endless belts flat throughout their travel in the casting section of the machine.

In the operation of the Hazelett machine for the production of a continuous strip of cast metal the metal belts must be, and run, flat during the casting and solidification operations. Further, the metal belts must provide the correct degree of resistance to heat transfer which, in turn, varies with the metal alloy being cast.. It has been found desirable in such a continuous metalcasting operation to protect the metal surfaces of the belts against unduly high temperatures to prevent distortion of the belts due to thermal expansion. Further, since the metal belts are run under tension and are flexed as they pass over pulleys any insulative, protective dressing employed thereon must not only be temperature resistant, i.e. refractory, but must be flexible and adherent to the metal surface of the belt to which the dressing is applied.

In the past it has been the practice to coat the metal surfaces of the belts in contact'with the molten metal with an organic resin, such as a polyvinyl butyral resin containing a metal chromate, e.g. zinc chromate, dispersed therein. A suitable organic resin composition and properties thereof are described in Canadian Government Specifications Board lGPl21 and also in US. 2,488,651, issued November 22, 1949, which discloses primer coa 3,1633% Patented Jan. 5, 1965 ings comprising solutions of vinyl resins having hydroxyl groups, in particular polyvinyl partial butyral resins, and an insoluble basic zinc chromate as a pigment. When phosphoric acid is added to a vinyl resin solution of this type, a composition is obtained from which an adherent film can be deposited on metals after air-drying, provided the resulting admixture is timely used. The disclosures of this patent are herein incorporated and made part of this disclosure. It has also been proposed to improve the heat resistance or high temperature properties of such resins when employed as a belt dressing by incorporating therein various silicone resins and the like. Other types of organic resins or belt coating material have been proposed and/ or used, such as phenolic and amino resin cured epoxy resins, e.g. Epon 1007 sold by Shell Chemical Corporation.

It has also been the practice to incorporate in these resins various amounts of solid, refractory, insulative material such as diatomaceous earth or diatomaceous silica and the like, e.g. Snow Floss sold by The Johns-Manville Company. These resulting compositions containing finely divided, refractory insulative material together with an organic resin as a binder can be sprayed onto the belts to provide a coating thereon having a thickness in the range 0.00l"0.005" (dry film). These coatings, hot ever, regardless of the organic resin or combination of organic resins or the solid insulative materials employed therein do not possess the high temperature properties and the degree of thermal stability whichwill enable them to withstand the impingement of molten metal, such as molten aluminum, for a satisfactory length of time. Such operational success as may have been experienced in the use of these materials has been, it appears due to the fact that when the organic resin material in the coating is destroyed or thermally decomposed by contact with the hot molten metal, an insulative layer of substantially only diatomaceous earth or similar refractory material is left behind. This layer insulates the deeper layers of organic resin'material that may still remain on the belt and prevents these layers from reaching temperatures at which the organic resin therein would thermally decompose. It is also thought that such preservation of the integrity of the deeper layers of the organic resein material is assisted during the metal casting operation by cooling the other side of the metal belt. In the Hazelett continuous metal casting process a temperature gradient through the dressing and belt is maintained so that the surface layers of the dressing in substantially direct contact with the molten metal are destroyed, leaving behind in their place an insulative layer of refractory powder-like diatomaceous silica, while the more remote organic resin layers immediately adjacent the metal surface of the belt are relatively cool and remain intact, flexible and adherent to the belt.

Further, in organic belt dressings employed heretofore certain other deficiencies have been observed, notably the tendency of the dressings to burn in unevenly, thus giving rise to dilferences in thermal conductivity or insulation in various areas of the dressed belt together with uneven freezing or solidification of the molten metal with corresponding defects in the finished cast metals. This particular deficiency can be reduced to some extent, but not satisfactorily eliminated, by prebaking the dressed belts for about one-half hour at 500 C. Also, uneven burn in can aggravate any tendency a belt may have to distort at an elevated temperature and such distortion, 7

when it occurs, produces characteristic defects in the finished cast metal strip.

Accordingly, it is an object of this invention to provide an improved dressing or dressing composition suitable for coating surfaces of a mold, such as a metal mold, in a metal casting operation.

It is another object of this invention to provide an Another object of this invention isto provide an improved coated continuous strip or belt suitable for use in a continuous metal casting operation.

Yet another object ofthis invention is to provide an I improved coating composition for coating metal forms, such as the surfaces of continuous metal strips or belts, to be employed in a metal casting operation in contact with molten metal.

How these and other objects of this invention are achieved will become apparent in the light of the accompartying disclosure made with reference to the accon panying drawings wherein:

FIG. 1 schematically illustrates the Hazelett continuous metal strip casting process and machine therefor; and

FIGS. 2 and 3 are cross-sectional views of a continuous metal belt coated with an improved coating composition in accordance with this invention.

It has now been discovered that a coating of relatively finely divided, fibrous alumino-silicate material provides an excellent insulative coating for mold surfaces, such as the surfaces of metal molds or metal belts, which are employed in a metal casting operation. Stillmore particularly, it has been found that finely divided, fibrous alumino-silicate when deposited on a surface of a mold,

such as on the surfaces of the continuous metal belts below about 5% by weight, of the fibrous alumino-silicate 1 coating, of an organic resin binder to serve to improve the adhesion of the fibrous. alumino-silicate coating onto the coated surface and also to impart flexibilty to the fibrous alumino-silicate coating. 7

In actual practice it has been found desirable to precoat the surface to be coated with an organic resinto serve as a base material or base layer. thereon since, apparently, better adhesion and flexibility of the fibrous 'alumino-silicate coating in accordance with'this invention is achieved when an organic resin coating or layer is placed intermediate the surface to be coated and the externalfibrous alumino-silicate coating.

silicate coating which contribute to the insulative properties of the fibrous alumino-silicate coating. This type of coating has been found to be particularly desirable for the production of high quality, cast metal strip.

The fibrous alumino-silicate coating is deposited by any suitable means or method, such as by brushing or wiping the fibrous alumino-silicate containing coating composition, onto the surface to be coated. It is preferred, however, to spray the fibrous alumino-silioate coating compositiononto the surface to be coated. When a priming coat is employed as an intermediate coating, in addition to the external alumino-silicate coating, the dry film thickness of the priming coat is usually about 0.0005". The thickness of the external fibrous alumino-silicate coating is usually about 0.002 (dryfihn thickness).

Referring now to FIG. 1 which schematically illustrates the application of this invention to the Hazelett continuous metal strip casting process and machine, molten metal, such as molten aluminum or molten aluminum alloy, is supplied from a suitable source, not shown, via feed box or spout 10 at one end of the casting machine into the space between continuously moving belts 11 and 12. In accordance with the invention the opposed surfaces of belts 11 and 12 in contact with the molten metal are coated with a fibrous alu'mino-silicate coating. The illustration of the machine in FIG. 1 is purely diagrammatic, it being understood that whereas the arrangement of belt rolls or pulleys somewhat follows that of the cited Patent No.

2,640,235, other arrangements can be and are used, as may be desired. Ashere shown, belt 11 passes over tension roll 14 and driving roll 15, while belt 12 passes over tension roll 16 and drivingroll 18. At the metal feed end, appropriate means, shown as guide rolls 19 and 20, bring the belts together to form a vessel for the metal 21, it being understood that throughout the metal-receiving and casting region the pair of belts is flanked by traveling dams or walls (not shown) whereby the metal, as it cools, is continuously retained in a rectangular region defining the cross-section of the strip to be produced.

As generally indicated'in FIG. 1, belts 11 and 12 move continuously and synchronously, while cooling water, from means not shown, is flushed across the upper surface of belt 12 and the lower surface of belt 11', along the region where the metal is carried between them. An appro- Particularly suitable as the intermediate coating or layer, so-calledpriming coat, is a polyvinyl butyral resin a may include a minor amount of silicone resin, such as Dow Corning Z-6018 admixed therewith. Other types of organic resin may also be employed in or make up the priming coat, such as phenolic and amino-cured epoxy resins.

The fibrous alumino-silicate coating comprises 'a matte of intimately-interwoven, finely divided, fibrous aluminosilicate having a fiber length substantially below 0.25 inch, such as a fiber length in the range .0.00010.-1, more or less. The fibrous. alumino-silicate' coating provides a dull, microscopically roughened coarse surface so that.

when molten metal is deposited and solidifies thereon the surface is bridged by the metal as it freezes to provide numerous air pockets onthe surface of the alumino-v priate series of rolls, preferably closed spaced, but here indicated simply by the guide rolls 19, 20, and further sizing rolls 22, 24, press against the opposite sides of belts 12,11 respectively, throughout the cooling and solidifying region, and serve to maintain (adjustably, if desired) the selected, predetermined distance between the belts, depending upon the thickness desired in the resulting cast strip 25 which is continuously removed from between belts 11 and 12 at the other end of the machine at driving pulleys 15 and 18,]as indicated. It is thus seen that the endless metal bolts 11 and 12,-usually manufactured of mild steel, are protected against contact with the hot molten metal by the coating of fibrous alumino-silicate deposited thereon so that no bare metal surface. of metal belts 11 and i2 is exposed to direct contact with the molten metal.

Refeiring now to FIG. 2 of thedrawings, there is illustrated therein a somewhat schematic cross-sectional view of an endless metal belt coated on one side or surface with the fibrous alumino-silicate coating 31 prepared and deposited on steel belt 30 in accordance with this invention. Similarly, FIG. 3 is a cross-sectional viewof an endless metal belt 30 provided on one side or surface with an intermediate, organic priming coat 32 upon which is deposited a fibrous alumino-silicate coating 31 prepared and deposited in accordance with this invention.

The following is exemplary of the practice of this invention. The fibrous alumino-silicate coating composition is prepared and deposited on the surface to be coated in accordance with the following procedure. There is Pi pa e an aq eous fibrous alumino-silicate coating ad-,

mixture comprising 700 parts by weight water, 16 parts by weight of a nonionic surfactant, such as an alkylphenoxypoly (ethyleneoxy) ethanol, specifically a nonylphenoxypoly (ethyleneoxy) ethanol, e.g. Igepal CO-630, 160 parts by weight of a water-dispersible polyacrylic resin, such as a water-dispersible polyacrylate, e.g. Rhoplex 13-15, and 800 parts by weight of an aqueous solution containing finely-divided fibrous alumino-silicate dispersed therein, such as an aqueous solution containing a minor amount by weight borax dissolved therein, and about 70% by weight fibrous alumino-silicate. A suitable aqueous solution containing fibrous alumino-silicate dispersed therein is commercially available and manufactured and sold by Carborundum Co. under the trademark Fiberfrax QF-180.

The resulting coating admixture is applied onto the surface to be coated over a priming coat, the amount of coating admixture applied being sufiicient to deposit on the resulting coated surface a fibrous alumino-silicate coating having a dry film thickness of 0.002 inch. After a suitable length of time, at least about 4 hours at 75 C., to permit drying of the thus-deposited fibrous aluminosilicate coating admixture, the resulting coated material is ready for use.

As is apparent from the foregoing disclosure the essential ingredient of the coating composition of this invention is finely-divided, fibrous alumino-silicate. The material is best employed in aqueous admixture in the form of an aqueous paste or an aqueous suspension wherein the finely-divided fibrous alumino-silicate is admixed or dispersed or suspended in an aqueous boroncontaining or borax-containing solution wherein the fibrous alumino-silicate is present in a major amount, above about 50% by weight, based on the resulting admixture. A suitable suspension of fibrous alumino-silicate material is an aqueous suspension thereof containing about 69% by weight solids, principally fibrous alumino-silicate, weighing about 14 pounds per gallon, having a viscosity at 25 C., in the range 4-6000 cps. and having the appearance of heavy cream. Additionally, the solids contained in the admixture have the following chemical analysis:

In the preparation of the coating admixture, as indicated hereinabove, there is also desirably included therein a minor amount of a surfactant, desirably a non-ionic surfactant, in an amount in the range below about 2% by weight, such as an amount in the range 0.1-1.5% by weight, suflicient to improve the fluidity and wettability of the resulting admixture and to disperse and maintain the fibrous alurnino-silicate in aqueous suspension.

There is desirablyincluded in the coating admixture a compatible, water-dispersible organic resin having a solid content in the range 30-75% by weight, more or less, such as a polyacrylate or polymethacrylate or a polymethylmethacrylate, in a minor amount, such as an amount in the range 2-10% by weight, more or less, sufficient to serve as a binder of the fibrous alumino-silicate and to impart flexibility to the resulting formed coating. A particularly suitable organic resin is a water-dispersible polyacrylate sold under the trademark Rhoplex B-15 by Rohm & Haas and having a solids content of about 46% by weight. Other water-dispersible organic resin compositions are known, as indicated herein, and are suitable for use in the preparation of coating admixtures and in coating compositionsin accordance with this invention.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many modifications, alterations and substitutions are possible in the practice of this invention without departing from the spirit or scope thereof.

We claim:

1. An article of manufacture suitable for use in the continuous casting of aluminum-containing metal comprising a flat, endless mild steel belt, the outside surface of said belt being provided with a priming coat comprising polyvinyl butyral resin containing finely-divided zinc chromate dispersed therein and a second coat deposited on said priming coat and comprising fibrous aluminosilicate, said alumino-silicate having a fiber length below 0.25, the thickness of said second coat comprising fibrous alumino-silicate being about 0.002.

2. In a metal casting operation wherein molten aluminum-containing metal is introduced between two opposed, continuously moving, endless steel belts, the opposed surfaces of said belts serving as a mold, and the thus-introduced molten metal solidified between the opposed surfaces of said moving belts, the improvement which comprises providing a coating on said opposed surfaces, said coating being provided by forming on the surface of said belt to be coated a priming coat comprising polyvinyl butyral resin containing finely divided zinc chromate dispersed therein and depositing a second coat on said priming coat, said second coat comprising fibrous alumino-silicate, said alumino-silicate having a fiber length below 0.25 inch, the thickness of said second coat comprising fibrous alumino-silicate being about 0.002

inch. I

3. A method in accordance with claim 2 wherein said second coat containing fibrous alumino-silicate contains borax and an organic resin binder for the fibrous alumino-silicate therein.

4. A method in accordance with claim 3 whereinsaid organic resin is a water-dispersible polyacrylate.

5. A method in accordance with claim 3 wherein said organic resin is a water-dispersible epoxy resin.

6. A method in accordance with claim 3 wherein said organic resin is a water-dispersible polymethacrylate.

7. A method in accordance with claim 3 wherein said organic resin is a water-dispersible polymerized methyl methacrylate.

References (Iited in the tile of this patent UNITED STATES PATENTS 2,311,233 Iaenicke et al Feb. 16, 1943 2,488,651 Whiting Nov. 22, 1949 2,578,976 Ingala Dec. 18, 1951 2,640,235 Hazelett June 2, 1953 2,645,558 Burchartz July 14, 1953 2,852,821 Pond Sept..23, 1958 2,904,860 Hazelett Sept. 22, 1959 2,907,084 7 Wood Oct. 6, 1959 2,911,505 Legg et al. Nov. 3, 1959 2,988,851 Holscher June 20, 1961 3,013,901 Bugosh Dec. 19, 1961 3,077,413 Campbell Feb. 12, 1963 FOREIGN PATENTS 229,416 Australia July 20, 1960 785,823 Great Britain Nov. 6, 1957 792,040 Great Britain Mar. 19, 1958 

1. AN ARTICLE OF MANUFACTURE SUITABLE FOR USE IN THE CONTINUOUS CASTING OF ALUMINUM-CONTAINING METAL COMPRISING A FLAT, ENDLESS MILD STEEL BELT, THE OUTSIDE SURFACE OF SAID BELT BEING PROVIDED WITH A PRIMING COAT COMPRISING POLYVINYL BUTYRAL RESIN CONTAINING FINELY-DIVIDED ZINC CHROMATE DISPERSED THEREIN AND A SECOND COAT DEPOSITED ON SAID PRIMING COAT AND COMPRISING FIBROUS ALUMINOSILICATE, SAID ALUMINO-SILICATE HAVING A FIBER LENGTH BELOW 0.25", THE THICKNESS OF SAID SECOND COAT COMPRISING FIBROUS ALUMINO-SILICIATE BEING ABOUT 0.002". 